Disk drive operable with first and second servo patterns in a perpendicular media recording environment

ABSTRACT

A disk drive operable with first and second servo patterns in a perpendicular media recording (PMR) environment is disclosed. The disk drive comprises a head operable with a perpendicular flux, a disk, and a servo controller. The disk includes a plurality of tracks, wherein each track has a plurality of servo sectors utilized in seek operations. The servo sectors of the disk include a first servo pattern between one of an inner diameter (ID) or an outer diameter (OD) of the disk and a middle diameter (MD) of the disk, respectively, and a second servo pattern between the other of the OD or the ID of the disk and the MD of the disk, respectively. The servo controller operates in a first mode when seeking within one of the first or second servo patterns and a second mode when seeking between the first servo pattern and the second servo pattern.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and hereby cross-referenced with anapplication Ser. No. 11/525,411 entitled “System and Method for WritingServo Sectors in a Perpendicular Media Recording Environment”, filed onthe same day by inventors Chen et al., the disclosure of saidapplication being hereby incorporated by reference, both applications tobe assigned to Western Digital Corporation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates a disk drive operable with first andsecond servo patterns in a perpendicular media recording environment.

2. Description of the Prior Art and Related Information

Today, computing devices such as personal computers, personal digitalassistants, cell-phones, etc., are routinely used at work, at home, andeverywhere in-between. Computing devices advantageously enable the useof application specific software, file sharing, the creation ofelectronic documents, and electronic communication and commerce throughthe Internet and other computer networks. Typically, each computingdevice has a storage peripheral such as a disk drive.

A huge market exists for disk drives for mass-market computing devicessuch as desktop computers and laptop computers, as well as small formfactor (SFF) disk drives for use in mobile computing devices (e.g.personal digital assistants (PDAs), cell-phones, digital cameras, etc.).To be competitive, a disk drive should be relatively inexpensive andprovide substantial capacity, rapid access to data, and reliableperformance.

Disk drives typically employ a moveable head actuator to frequentlyaccess large amounts of data stored on a disk. One example of a diskdrive is a hard disk drive. A conventional hard disk drive has a headdisk assembly (“HDA”) including at least one magnetic disk (“disk”), aspindle motor for rapidly rotating the disk, and a head stack assembly(“HSA”) that includes a head gimbal assembly (HGA) with a moveabletransducer head for reading and writing data. The HSA forms part of aservo control system that positions the moveable transducer head over aparticular track on the disk to read or write information from and tothat track, respectively.

Typically, a conventional hard disk drive includes a disk having aplurality of concentric tracks. Each surface of each disk conventionallycontains a plurality of concentric data tracks angularly divided into aplurality of data sectors. In addition, special servo information may beprovided on each disk to determine the position of the moveabletransducer head.

The most popular form of servo is called “embedded servo” wherein theservo information is written in a plurality of servo sectors that areangularly spaced from one another and are interspersed between datasectors around each track of each disk.

Each servo sector typically includes a phase lock loop (PLL) field, aservo synch mark (SSM) field, a gray-coded track identification (TKID),a sector ID field having a binary encoded sector ID number to identifythe sector, and a group of servo bursts (e.g. an alternating pattern ofmagnetic transitions) which the servo control system of the disk drivesamples to align the moveable transducer head with or relative to aparticular track. Typically, the servo control system moves thetransducer head toward a desired track during a course “seek” mode usingthe gray-coded TKID field as a control input.

When manufacturing a disk drive, servo sectors are typically written tothe disk in order to define a plurality of evenly-spaced, concentrictracks. As previously discussed, a typical servo wedge includes a PLLfield, a SSM field, a gray-coded TKID field, and a wedge ID field.

Servo writers are typically used to write the servo sectors to the disksurface during manufacturing. Servo writers may employ extremelyaccurate head positioning mechanics, such as laser interferometers oroptical encoders, to ensure that the servo sectors are written at theproper radial location, typically, from the inner diameter of the diskto the outer diameter of the disk. In addition, extremely accurateclocking systems may be utilized in order to write the servo sectors inthe proper circumferential locations on the disk. Servo-writing mayoccur both in-situ utilizing the disk drive itself or just the HDA ofthe disk drive to write the servo-sectors, or servo-writing may beperformed on a disk in an external environment.

As previously discussed, the disk drive industry is very competitive anddisk drives are continually being sought after by consumers that providesubstantial capacity and rapid access to data. In order to meet consumerdemand for increased capacity and faster access to data, a new form ofmedia recording, entitled perpendicular media recording (PMR) is nowbeing utilized in order to increase the amount of data that can bestored on a disk.

Perpendicular media recording (PMR) allows hard disk drive manufacturersto put more bits of data on each square inch of disk because of magneticgeometry. In perpendicular media recording, writing on the magneticmedia occurs in a fashion in which the bits are aligned vertically,perpendicular to the disk, rather than parallel to the media as iscurrently done. By writing bits of data in a vertical fashion, higherrecording densities on the disk are enabled because bits of data can bepacked closer together.

Further, by utilizing perpendicular media recording (PMR) an improvementresults in that bits are better able to retain their magnetic charges, aproperty called coercivity. This helps to alleviate the “flipped bit”problem associated with standard parallel recording techniques. Due tothe ever increasing bit density provided on disk media utilizingstandard parallel recording techniques, bits are being written closerand closer together to improve disk density, such that when randomthermal vibrations occur bits may be “flipped”—in which the magneticnorth and south poles of bits are suddenly and spontaneously reversed,resulting in corrupted data.

Although perpendicular media recording (PMR) offers vast advantages inthe amount and reliability of data that can be stored on a disk of adisk drive, there is presently a problem in servo writing disksutilizing PMR technology due to the PMR disk head's footprint andsensitivity to skew angle in writing servo sectors to a disk.

For example, in utilizing conventional servo writing techniques with aPMR head, servo writing typically occurs in a single direction.Unfortunately, a problem occurs in that the written-in servo sector maybecome unreadable at large skew angles due to the footprint of the PMRhead. For example, when servo-writing in a single direction from theinner diameter (ID) of the disk to the outer diameter (OD) of the disk,as is commonly done, servo sectors may become unreadable at the OD sideof the disk.

More particularly, when servo-writing in a single direction utilizing aPMR head, at large skew angles, written-in servo sectors and the graycoded TKIDs contained therein used for seek operations may becomeunreadable resulting in wasted disk space and potential problems fordisk drive operations.

SUMMARY OF THE INVENTION

The present invention relates to a disk drive operable with first andsecond servo patterns in a perpendicular media recording (PMR)environment.

In one embodiment of the present invention, a disk drive operable withfirst and second servo patterns in a perpendicular media recording (PMR)environment is disclosed. The disk drive comprises a moveable headoperable with a perpendicular flux, a disk, and a servo controller. Thedisk includes a plurality of tracks, wherein each track has a pluralityof servo sectors utilized in seek operations. The servo sectors of thedisk include a first servo pattern between one of an inner diameter (ID)or an outer diameter (OD) of the disk and a middle diameter (MD) of thedisk, respectively, and a second servo pattern between the other of theOD or the ID of the disk and the MD of the disk, respectively. The servocontroller controls seek operations with the moveable head. The servocontroller operates in a first mode when seeking within one of the firstor second servo patterns and a second mode when seeking between thefirst servo pattern and the second servo pattern.

In another embodiment of the present invention, a method for performingseek operations in a disk drive is disclosed. The method comprisesmoving a head operable with a perpendicular flux relative to a disk. Thedisk includes a plurality of tracks and each track includes a pluralityof servo sectors utilized in seek operations, wherein the servo sectorsof the disk include a first servo pattern between one of an innerdiameter (ID) or an outer diameter (OD) of the disk and a middlediameter (MD) of the disk, respectively, and a second servo patternbetween the other of the OD or the ID of the disk and the MD of thedisk, respectively. The method further comprises controlling themovement of the head in both a first mode and a second mode to performseek operations, wherein, in the first mode, the movement of the headfor a seek operation is within one of the first or second servo patternsand, wherein, in the second mode, movement of the head for a seekoperation is between the first servo pattern and the second servopattern.

In yet another embodiment of the present invention, a disk drive isdisclosed, in which the disk drive includes a head andprocessor-readable medium having stored thereon instructions which whenexecuted by a processor of the disk drive, causes the disk drive toperform a plurality of operations. Particularly, the processor-readablemedium instructions, when executed by the processor of the disk drive,causes the disk drive to perform operations comprising: moving a headoperable with a perpendicular flux relative to a disk, in which the diskincludes a plurality of tracks and each track includes a plurality ofservo sectors utilized in seek operations, wherein the servo sectors ofthe disk include a first servo pattern between one of an inner diameter(ID) or an outer diameter (OD) of the disk and a middle diameter (MD) ofthe disk, respectively, and a second servo pattern between the other ofthe OD or the ID of the disk and the MD of the disk, respectively; andcontrolling the movement of the head in both a first mode and a secondmode to perform seek operations, wherein, in the first mode, themovement of the head for a seek operation is within one of the first orsecond servo patterns and, wherein, in the second mode, movement of thehead for a seek operation is between the first servo pattern and thesecond servo pattern.

The foregoing and other features are described in detail in the DetailedDescription and are set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is block diagram illustrating an example of a servo track writer(STW), in which embodiments of the invention related to a system andmethod for writing servo sectors in a perpendicular media recording(PMR) environment to a disk may be employed.

FIG. 2 is a diagram of a disk that illustrates servo sectors writtenonto a disk in a PMR environment, according to one embodiment of thepresent invention.

FIG. 3 is a graph illustrating physical gray coded TKID values of servosectors (Y-axis) versus tracks (X-axis) and also illustrates the strokedirection of the servo-writing, according to one embodiment of thepresent invention.

FIG. 4 is a diagram illustrating an example of a gray-coded TKID servopattern discontinuity that occurs due to the buffer zone, according toone embodiment of the present invention.

FIG. 5 shows a simplified block diagram of a disk drive, in whichembodiments of the invention may be practiced.

FIG. 6 is a flow diagram illustrating a process that the servocontroller may utilize for seek operations utilizing a disk having abuffer zone, according to one embodiment of the present invention.

FIGS. 7A and 7B are diagrams illustrating examples of the process thatthe servo controller may utilize for seek operations utilizing a diskhaving a buffer zone, according to one embodiment of the presentinvention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures, and techniques have not been shown in order not toobscure the understandings of this description.

With reference to FIG. 1, FIG. 1 is block diagram illustrating anexample of a servo track writer (STW), in which embodiments of theinvention related to a system and method for writing servo sectors in aperpendicular media recording (PMR) environment to a disk, may beemployed.

As shown in FIG. 1, a servo track writer (STW) 21 may operate in anin-situ environment 10, in which the STW 21 may be employed to writeservo sectors and other servo information to one or more disks 14 of anHDA 17 of a disk drive 12. Alternatively, in some embodiments, the STWmay operate only upon an HDA. It should be appreciated that this is avery simplified illustration of an HDA, and many components are notshown and are not discussed, in order not obscure the embodiments of theinvention. Further, hereinafter servo-writing will be discussed withreference to disk 14, however, it will be appreciated by those of skillin this art that one more disks 14 may be simultaneously or seriallywritten to.

Disk drive 12 may comprise a head disk assembly (HDA) 17 that includes adisk 14, an actuator arm 18, a perpendicular magnetic recording (PMR)head 20 coupled to a distal end of the actuator arm 18, and a voice coilmotor (VCM) 16 for rotating the actuator arm 18 about a pivot toposition PMR head 20 radially over disk 14. As will be described, PMRhead 20 writes servo sectors onto the disk 14 with a perpendicular fluxsuch that STW is a PMR STW.

The PMR STW 21 may employ a write clock that is synchronized to therotation of the disk 14 such that a plurality of servo sectors may bewritten onto the disk 14 at pre-determined radial locations, as will bedescribed. In this embodiment, PMR STW 21 comprises a head positioner 22for actuating a head positioning pin 23 using sensitive positionmeasurement circuitry, such as a laser interferometer or an opticalencoder. Pattern circuitry 24 generates a data sequence written to thedisk 14 for the servo sectors.

An optical or magnetic clock head 46 reads an optical or magnetic clocktrack to generate a clock signal 47 processed by timing circuitry 25 tosynchronize a write clock signal 26 so that servo sectors are written atappropriate radial positions on the disk 14. This optical or magneticclock track may be formed at the outside radius of at least one disk, orit may also be formed at the inside radius of at least one disk, or itmay be formed or written on some other rotating member of the disk drivesuch as the spindle motor, hub or disk attachment clamp.

PMR STW 21 under the control of control processor 30 controls the HDA 17such that actuator arm 18 is rotated to position the PMR head 20radially over disk 14 in order to write servo sectors onto disk 14 basedupon the output clock signal 26 that has been processed by timingcircuitry 25. In this way, a pre-determined sequence of servo-sectorsmay servo-written to a disk 14.

It should be appreciated that the PMR STW 21 may be utilized with acomplete disk drive or just an HDA of a disk drive. It should further beappreciated that many other types of servo track writers (STWs) may beutilized with embodiments of the invention for a system and method forwriting servo sectors in a perpendicular media recording (PMR)environment. For example, in another embodiment, an external PMR STW maybe utilized in an external media writing environment such as a cleanroom. For example, in an external media writing environment, multipledisks may be servo written without having to be located in the HDA of adisk drive or within a disk drive itself.

In one embodiment, under the control of control processor 30 and basedupon write clock signal 26 and the other components of PMR STW 21, headpositioner 22 positions PMR head 20 relative to disk 14 such that PMRhead 20 writes servo sectors onto the disk 14 from one of an innerdiameter (ID) or an outer diameter (OD) of disk 14 to a middle diameter(MD) of disk 14, respectively, followed by writing servo sectors betweenthe other of the OD or the ID of disk 14 to the MD of disk 14,respectively.

With reference also to FIG. 2, a diagram of a disk 14 is shown thatillustrates servo sectors 2 _(0-N) written onto disk 14 in a PMRenvironment according to embodiments of the invention. As is known, whenmanufacturing a disk drive, servo sectors 2 ₀-2 _(N) are written to disk14 in order to define a plurality of evenly-spaced, concentric tracks 6.

Each servo sector 2 may include a phase lock loop (PLL) field 7, a servosynch mark (SSM) field 8, a track identification (TKID) field 9, asector ID 10, and a group of servo bursts (e.g. ABCD) 11, (e.g. analternating pattern of magnetic transitions), that the servo controlsystem of the disk drive samples to align the moveable transducer headwith, and relative to, a particular track 6.

Each circumferential track 6 includes a plurality of embedded servosectors 2 _(0-N) utilized in seeking and track following. The pluralityof servo sectors 2 _(0-N) are spaced sequentially around thecircumference of a circumferential track 6 and extend radially outwardfrom the inner diameter (ID) 31 of the disk 14. These embedded servosectors 2 contain servo information utilized in seeking and trackfollowing and are interspersed between data regions 3 of the disk 14.Data is conventionally written in the data regions 3 in a plurality ofdiscrete data sectors. Each data region 3 is typically preceded by aservo sector 2.

The PMR STW 21 under the control of controller 30 utilizes headpositioner 22 to position the PMR head 20 relative to disk 14 andcontrols head positioner 22 such that PMR head 20 writes servo sectors 2_(0-N) onto disk 14 from one of inner diameter (ID) 31 or outer diameter(OD) 32 of the disk 14 to middle diameter (MD) 33 of disk 14,respectively, followed by writing servo sectors 2 _(0-N) between theother of the OD or the ID of the disk to the MD of the disk,respectively.

As an example, in this embodiment, a first servo pattern 36 is createdbetween the ID 31 and the MD 33 of the disk and a second servo pattern38 is created between the OD 32 and the MD 33 of disk 14. The firstservo pattern 36 includes a first plurality of gray-coded servo patternsaligned with a starting point from the ID 31 and the second servopattern 38 includes a second plurality of gray-coded servo patternsaligned with a starting point from the OD 32 such that the first andsecond plurality of gray-coded servo patterns 36 and 38 are offset fromone another as shown in FIG. 2.

It should be appreciated that the PMR STW 21 can either write servosectors 2 _(0-N) from the ID 31 to the MD 33 and then from the OD 32 tothe MD 33 or from the OD 32 to the MD 33 and then from the ID 31 to theMD 33. For ease of reference, it will be assumed that the PMR STW 21writes the servo sectors 2 _(0-N) from the ID 31 to the MD 33 followedby the OD 32 to the MD 33. However, it should be appreciated that eithermethod is suitable.

Particularly, utilizing this methodology, a buffer zone 40 is createdbetween the first servo pattern 36 and the second servo pattern 38. Thebuffer zone 40 includes an area that has been written to with both thefirst servo pattern 36 and the second servo pattern 38. The buffer zone40 is particularly illustrated in FIG. 2.

The location of the buffer zone 40 may be stored in the disk drive 12associated with the disk 14 that has been servo-written to in thismanner. In some embodiments, the buffer zone 40 may be less thanapproximately three-hundred tracks wide.

Also, although not particularly described, it should be appreciated thatthe PMR head 20 may be of many different shapes and geometries as PMRtechnology is continually evolving. In one embodiment, the PMR head 20may be approximately trapezoidally-shaped.

It should also further be appreciated that, in one embodiment, the PMRSTW 21 may include a processor-readable medium having stored thereoninstructions which when executed by the control processor 30 of the PMRSTW 21, causes the PMR STW 21 to perform a plurality of operations.Particularly, the processor-readable medium instructions, when executedby the control processor 30 of the PMR STW 21, may cause the PMR STW 21to perform operations comprising: moving the head positioner 22 toposition the PMR head 20 of the HDA 17 relative to the disk 14;commanding the PMR head 20 to write servo sectors 2 _(0-N) onto the disk14, wherein PMR head 20 writes servo sectors 2 _(0-N) onto disk 14 witha perpendicular flux; and controlling the movement of PMR head 20 withthe head positioner 22 such that PMR head 20 write servo sectors 2_(0-N) onto disk 14 from one of the ID 31 or the OD 32 of the disk tothe MD 33 of the disk, respectively, followed by writing servo sectors 2_(0-N) between the other of the OD 32 or the ID 31 of the disk to the MD33 of disk 14, respectively.

For the purposes of the present specification, it should be appreciatedthat the terms “processor”, “microprocessor”, and “controller”, etc.,refer to any machine or collection of logic that is capable of executinga sequence of instructions and shall be taken to include, but not belimited to, general purpose microprocessors, special purposemicroprocessors, central processing units (CPUs), digital signalprocessors (DSPs), application specific integrated circuits (ASICs),multi-media controllers, signal processors and microcontrollers, etc.

Components of the various embodiments of the invention may beimplemented as hardware, software, firmware, microcode, or anycombination thereof. When implemented in software, firmware, ormicrocode, the elements of the embodiment of the present invention arethe program code or code segments that include instructions to performthe necessary tasks. A code segment may represent a procedure, afunction, a subprogram, a program, a routine, a subroutine, a module, asoftware package, a class, or any combination of instructions, datastructures, or program statements.

Turning now to FIG. 3, FIG. 3 is a graph 300 illustrating physical graycoded TKID values of the servo sectors (Y-axis) 302 versus the tracksfrom the OD to the ID of the disk (X-axis) and also illustrates thestroke direction of the servo-writing. In this example, as shown in FIG.3, the first stroke 310 is from the ID 31 to the MD 33 and the secondstroke 320 is from the OD 32 to the MD 33.

More particularly, as previously discussed, the PMR STW utilizing thehead positioner moves the PMR head of the HDA relative to the disk fromthe ID 31 of the disk 14 to the MD 33 of the disk through the bufferzone 40 as represented by stroke line 310. Next, as represented bystroke line 320, the PMR STW utilizing the head positioner moves the PMRhead of the HDA relative to the disk from the OD 32 of the disk to theMD 33 of the disk through the buffer zone 40.

Thus, a first servo pattern is created between the ID 31 and MD 33 ofthe disk and a second servo pattern is created between the OD 32 and theMD 33 of the disk. Further, as shown in FIG. 3, a buffer zone 40 iscreated between the first servo pattern and the second servo patternproximate the MD 33 of the disk 14. The buffer zone 40 includes anoverlap region 45 that has been written to with both the first servopattern and the second servo pattern. As further shown in FIG. 3, thereis a discontinuity 47 associated with the buffer zone 40 and the overlapregion 45 between the gray coded TKID values 302.

Furthermore, as shown in FIG. 3, additional tracks 50 may beservo-written near the OD 32. This is because the servo-writing, as partof a second stroke 320, begins at the OD 32 and the footprint of the PMRhead and its sensitivity to skew angle is not as problematic such thatadditional readable servo sectors near the OD 32 may be written.

As can be seen in FIG. 3, a first servo pattern written by stroke 310with a starting point from the ID 31 and an ending point at a the end ofthe buffer zone 40 includes a first plurality of gray-coded TKID servopatterns 302 that are aligned with the starting point of the ID 31.Further, a second servo pattern written by stroke 320 with a startingpoint from the OD 32 and an ending point at the other end of the bufferzone 40 includes a second plurality of gray-coded TKID servo patterns302 that are aligned with the starting point of the OD 32. It should beappreciated that these gray-coded TKID servo patterns are off-set fromone another. Further, there is a discontinuity 47 between thesegray-coded TKID servo patterns, which occurs due to the buffer zone 40.

Turning briefly now to FIG. 4, FIG. 4 is a diagram illustrating anexample of this gray-coded TKID servo pattern discontinuity 47 thatoccurs due to the buffer zone. As shown in FIG. 4, there is a gray-codedTKID servo pattern discontinuity 47 between the first gray-coded TKIDservo pattern extending between the ID 31 and the approximate MD 33 andthe second gray-coded TKID servo pattern extending between the betweenthe OD 32 and the approximate MD 33 of the disk.

A system and method for a disk drive to take into account this bufferzone and gray code discontinuity will be hereinafter discussed.

It should be appreciated that by writing the servo sectors in a firstdirection from the ID to the MD of the disk and in a second directionfrom the OD to the MD of the disk that the servo sectors andparticularly the gray-coded TKIDs associated therewith are written in aconsistent and readable fashion. In this way, problems related towritten-in servo sectors that are unreadable due to the footprint of thePMR head and the large skew angles at which they are written, in singledirection servo-writing, are overcome by this dual directionservo-writing approach. Further, by this method, in this example, eventhough unusable servo sectors in the buffer zone are introduced, many orall of these unusable servo sectors may be replaced by thepreviously-described additional tracks that may be utilized at the OD,which in traditional single direction servo-writing cannot beservo-written to, due to the footprint of a typical PMR head and thelarge skew at the OD.

A disk drive that may operate with the previously-described formatteddisk having a first servo pattern and a second servo pattern, along witha buffer zone therebetween, will now be described.

FIG. 5 shows a simplified block diagram of disk drive 12, in whichembodiments of the invention may be practiced. Disk drive 12 comprises aHead/Disk Assembly (HDA) 17 and a controller printed circuit boardassembly (PCBA) 532. Host 536 may be a computing device 536 such as adesktop computer, a laptop computer, a mobile computing device (e.g.PDA, camera, cell-phone, etc.), or any type of computing device. Diskdrive 12 may be of a suitable form factor and capacity for largercomputers or for smaller mobile devices (e.g. a small form factor (SFF)disk drive).

The HDA 17 comprises: one or more disks 14 for data storage; a spindlemotor 550 for rapidly spinning each disk 14 (four shown) on a spindle548; and an actuator assembly 540 for moving a plurality of PMR heads 20in unison over each disk 14. As previously described, the head(s) ofdisk drive 12 may be PMR heads and may operate with perpendicular flux.Further, as previously described, the one or more disk(s) 14 may beformatted and servo-written, as previously discussed, with a PMRservo-writer such that they include a first servo pattern and a secondservo pattern, along with a buffer zone therebetween.

Actuator assembly 540 includes a plurality of actuator arms 18 havingPMR heads 20 attached to distal ends thereof, respectively, such thatthe actuator arms 18 and PMR heads 20 are rotated about a pivot point sothat the PMR heads sweep radially across the disks 14, respectively. ThePMR heads 20 are connected to a preamplifier 542 via a cable assembly565 for reading and writing data on disks 14. Preamplifier 542 isconnected to channel circuitry in controller PCBA 532 via read data line592 and write data line 590.

Controller PCBA 532 comprises a read/write channel 568, servo controller598, host interface and disk controller (HIDC) 574, voice coil motordriver (VCM) 16, spindle motor driver (SMD) 503, microprocessor 584, andseveral memory arrays—buffer or cache memory 582, RAM 508, andnon-volatile memory 506.

Servo controller 598 may operate under the control of a program orroutine, including a buffer zone compensation program 599, to executemethods or processes in accordance with embodiments of the invention.These embodiments relate to accounting for the previously-describedbuffer zone and compensating for the buffer zone in servo operations,such as seek operations. Further, microprocessor 584 may pre-programservo controller 598 and/or initialize the servo controller with initialand operational values for use in implementing the buffer zonecompensation program.

Host initiated operations for reading and writing data in disk drive 12are executed under control of microprocessor 584 connected to thecontrollers and memory arrays via a bus 586. Program code executed bymicroprocessor 584 is stored in non-volatile memory 506 and randomaccess memory RAM 508. Program overlay code stored on reserved tracks ofdisks 546 may also be loaded into RAM 508 as required for execution.

During disk read and write operations, data transferred by preamplifier542 is encoded and decoded by read/write channel 568. During readoperations, channel 568 decodes data into digital bits transferred on anNRZ bus 596 to HIDC 574. During write operations, HIDC provides digitaldata over the NRZ bus to channel 568 which encodes the data prior to itstransmittal to preamplifier 542. Preferably, channel 568 employs PRML(partial response maximum likelihood) coding techniques, although theinvention may be practiced with equal advantage using other codingprocesses.

HIDC 574 comprises a disk controller 580 for formatting and providingerror detection and correction of disk data, a host interface controller576 for responding to commands from host 536, and a buffer controller578 for storing data which is transferred between disks 546 and host536. Collectively the controllers in HIDC 574 provide automatedfunctions which assist microprocessor 584 in controlling disk driveoperations.

The servo controller 598 provides an interface between microprocessor584 and actuator assembly 540 and spindle motor 550. Microprocessor 584commands logic in servo controller 598 to position actuator assembly 540using a VCM driver 502 and to precisely control the rotation of spindlemotor 550 with a spindle motor driver 503.

Disk drive 12 may employ a sampled servo system in which equally spacedservo sectors are recorded on each track of each disk 14. Data sectorsare recorded in the intervals between servo sectors on each track. Servosectors are sampled at regular intervals by servo controller 598 toprovide servo position information to microprocessor 584. Servo sectorsare received by channel 568, and are processed by servo controller 598to provide position information to microprocessor 584 via bus 586.Further, servo controller 598 may operate under the control of a programor routine, such as a buffer zone compensation program 599 to executemethods or processes in accordance with embodiments of the inventionrelated to compensating for the previously-described buffer zone duringservo operations such as seek operations.

As previously described with respect to FIG. 2, disk 14 includes aplurality of concentric circumferential tracks 6. Each circumferentialtrack 6 includes a plurality of embedded servo sectors 2 _(0-N) utilizedin seeking and track following. The plurality of servo sectors 2 arespaced sequentially around the circumference of each circumferentialtrack 6. Each servo sector 6 contains servo information utilized inseeking and track following and are interspersed between data regions 3of the disk 14. Data is conventionally written in the data regions 3 ina plurality of discrete data sectors. Each data region 3 is typicallypreceded by a servo sector 2.

Also, as previously described, each servo sector 2 includes a phase lockloop (PLL) field 7, a servo synch mark (SSM) field 8, a trackidentification (TKID) field 9, a sector identifier (ID) 10, and a groupof servo bursts (e.g. ABCD) 11 (e.g. an alternating pattern of magnetictransitions), that the servo control system samples to align themoveable PMR head 20 with, and relative to, a particular track.Typically, servo controller 598 moves the PMR head 20 toward the desiredtrack during a course “seek” mode using the TKID field 9 as a controlinput.

In processing information, it may be necessary to ensure consistency inthe detection of bits composing a block of bits. In order to ensure suchconsistency, the phase lock loop (PLL) field 7 is first read in order tofacilitate bit synchronization. Next, the SSM field 8 is read tofacilitate block synchronization. The SSM field 8 facilitates a blocksynchronization by acting as a special marker that is detected to“frame” data (i.e., to identify a boundary of a block). A valid servosynchronization signal results in the read/write channel 568 of the diskdrive 12 establishing a precise timing reference point for the readingof servo data and for read/write operations. It is well known to provideframing of servo data via a SSM 8. The sector ID 10 may be a binaryencoded sector ID number to identify the sector of the track.

Further, once the PMR head 20 is generally over the desired track 6, theservo controller 598 uses the servo bursts (e.g. ABCD) 11 to keep thetransducer head over the track in a fine “track follow” mode. Duringtrack following mode, the moveable PMR head 20 repeatedly reads thesector ID 10 of each successive servo sector to obtain the binaryencoded sector ID number that identifies each sector of the track.

Based on the TKID 9 and sector ID 10, the servo controller 598continuously knows where the PMR head 20 is relative to the disk 14 andcommunicates this to microprocessor 584. In this way, the microprocessor584 continuously knows where the PMR head 20 is relative to the disk andcan command the movement of PMR head 20, via the servo control system,to implement disk drive operations, such as seeking, tracking,read/write operations, etc.

It should be noted that, as previously described with reference to FIG.2, that the servo sectors 2 that are servo written with PMR head 20 ontodisk 14, are, in one example, written first between the ID 31 of thedisk 14 to the MD 33 of the disk 14 to create a first servo pattern 36and are then written between the OD 32 and the MD 33 of the disk 14 tocreate a second servo pattern 38. The first servo pattern 36 includes afirst plurality of gray-coded servo patterns aligned with a startingpoint from the ID 31 and the second servo pattern 38 includes a secondplurality of gray-coded servo patterns aligned with a starting pointfrom the OD 32 such that the first and second plurality of gray-codedservo patterns are offset from one another. Moreover, each of the firstand second plurality of gray-coded servo patterns each includesgray-coded TKID fields associated with each respective servo sector.

Further, as previously discussed, a buffer zone 40 is created betweenthe first servo pattern 36 and the second servo pattern 38 wherein thebuffer zone 40 includes an area that has been written to with both thefirst servo pattern 36 and the second servo pattern 38. Generally, thebuffer zone 40 is present between the first servo pattern 36 and thesecond servo pattern 38 proximate the MD 33 of the disk.

Characteristics associated with the buffer zone 40 may be stored innon-volatile memory 506 (e.g. Flash memory) of disk drive 12 andprovided to the servo controller 598 and/or RAM 508 upon power up ofdisk drive 12. Further, servo controller 598 may store the buffer zonecharacteristics for use in servo operations, such as seek operations, aswill be discussed in more detail hereinafter. Buffer zonecharacteristics may include a buffer zone size, a buffer zone startingtrack identifier (TKID) and a buffer zone ending track identifier(TKID).

Servo controller 598 may operate under the control of a program orroutine, such as a buffer zone compensation program 599 to executemethods or processes in accordance with embodiments of the invention.Embodiments of the invention relate to implementing a buffer zonecompensation method in order to account for the buffer zone 40 inseeking between the first and second sets of servo patterns 36 and 38,respectively. As previously described, servo controller 598 is generallyresponsible for commanding seek and track follow operations via actuatorassembly 540 and PMR head 20.

Is should be appreciated that embodiments of the invention may beimplemented with servo controller and/or other circuitry, includingmicroprocessor 584. Particularly, circuitry of the disk drive, includingbut not limited to servo controller 598 and/or microprocessor 584, mayoperate under the control of a program or routine to execute methods orprocesses in accordance with embodiments of the invention.

For the purposes of the present specification, it should be appreciatedthat the terms “processor”, “microprocessor”, and “controller”, etc.,refer to any machine or collection of logic that is capable of executinga sequence of instructions and shall be taken to include, but not belimited to, general purpose microprocessors, special purposemicroprocessors, central processing units (CPUs), digital signalprocessors (DSPs), application specific integrated circuits (ASICs),multi-media controllers, signal processors and microcontrollers, etc.

Components of the various embodiments of the invention may beimplemented as hardware, software, firmware, microcode, or anycombination thereof. When implemented in software, firmware, ormicrocode, the elements of the embodiment of the present invention arethe program code or code segments that include instructions to performthe necessary tasks. A code segment may represent a procedure, afunction, a subprogram, a program, a routine, a subroutine, a module, asoftware package, a class, or any combination of instructions, datastructures, or program statements.

In one embodiment, servo controller 598 may control seek operations withmoveable PMR head 20. The servo controller 598 may operate in a firstmode when seeking within one of the previously-described first or secondservo patterns 36 or 38, respectively, and a second mode when seekingbetween the first and second servo patterns 36 and 38, respectively.Hereinafter servo pattern 36 will be referred to as the first servopattern and servo pattern 38 will be referred to as the second servopattern, however, it should be appreciated that this is merely forsimplicity and, alternatively, servo pattern 38 could be the first servopattern and servo pattern 36 could be the second servo pattern.

For example, in the first mode, servo controller 598 may control a seekoperation between a start track of servo pattern 38 and an end track ofthe same servo pattern 38. In this example, the buffer zone 40 does nothave to be taken into account because the servo controller 598 does nothave to seek across the buffer zone 40. In this example, as will bedescribed, the servo controller 598 does not have to utilize adjustedphysical gray coded TKID values versus logical TKID values.

On the other hand, in the second mode, the servo controller 598 controlsa seek operation between a start track of a servo pattern (e.g. secondservo pattern 38) and an end track of another servo pattern (e.g. firstservo pattern 36) and crosses and compensates for buffer zone 40 byutilizing adjusted physical gray code TKID values for the end track thataccounts for the buffer zone size versus logical TKID values.

Turning now to FIG. 6, FIG. 6 is a flow diagram illustrating a process600 that the servo controller may utilize for seek operations utilizinga disk 14 having a buffer zone 40.

Also, simultaneous reference may also be made to FIGS. 7A and 7B, whichillustrate a set of seeking examples (e.g. Example 1, Example 2, andExample 3) and associated commanded logical TKID values and actualphysical gray code TKID values to implement the seek operations.

At block 602 the seek operation performed by the servo controllerbegins. At block 604 the servo controller first determines whether thestart and end track are within the same servo pattern zone. This may bereferred to as the first mode.

In the first mode, the seek operation is within a servo pattern zonedefined by one of the first or second servo patterns (e.g. 36 or 38),previously discussed, and does not cross the buffer zone 40.

An example of this is illustrated in FIG. 7A as Example 1. If the seekoperation 702 is within a single servo pattern zone (e.g. second servopattern 38), then the servo controller initiates first mode processing(block 606). At block 608 the process ends.

Particularly, as seen in FIG. 7B, in Example 1, assuming as an examplethat the servo controller has been commanded to perform a seek operationfrom logical TKID 200 to logical TKID 400, the servo controller uses theunmodified gray code for the end track (i.e. physical gray code TKID400) and commands the actuator to move the PMR head by two hundredtracks to physical gray coded track ID 400 within the same servo patternzone.

Alternatively, if both the start and end track are in the other servozone (e.g. first servo pattern 36; with start logical TKID=800 and endlogical TKID=900) then first processing includes simply utilizingadjusted physical gray code values for both the start track and the endtrack (that already reflect the buffer zone) wherein start physical graycoded TKID=1300 and end physical gray coded TKID=1400. Thus, when theservo controller has been commanded to perform a seek operation fromlogical TKID 800 to logical TKID 900 (both in first servo pattern 36 onthe other side of the buffer zone 40), during first processing, theservo controller uses the modified gray code for the end track (i.e.physical gray code TKID 1400) and commands the actuator to move the PMRhead by one hundred tracks to physical gray coded TKID 1400 within thesame servo pattern zone.

It should be appreciated that these are simple exemplary numbers forillustrative purposes.

However, if the end track to be seeked to is not within the same servopattern zone, the servo controller next determines at decision block 620whether the end track is within the buffer zone 40. If so, the servocontroller adjusts the seek operation by utilizing an adjusted physicalgray code TKID value for the appropriate buffer zone boundary (block622). At block 623 the process ends.

An example of this is illustrated in FIGS. 7A and 7B, as Example 2. Ifthe starting track (e.g. track 200) is within a servo pattern zone (e.g.second servo pattern 38), and the servo controller commands the actuatorassembly to move the PMR head during a seek operation 708 from logicalstart TKID 200 to logical end TKID 500 (shown as point 710), which iswithin the buffer zone 40, the servo controller utilizes an adjusted ormodified physical gray coded TKID value, for example 1000, shown aspoint 712, at the other end of the buffer zone 40 (i.e. it is an IDbuffer zone boundary track). In this case, the servo controller movesthe PMR head eight hundred tracks instead of three hundred tracks suchthat the approximately five hundred track buffer zone size is accountedfor. In this way, the buffer zone is transparent to the rest of the diskdrive and the host.

It should be appreciated that these are simple numbers for illustrativepurposes only and the same or similar processes would work in oppositedirections, as well. For example, in moving the head from servo pattern36 to a commanded logical track that falls within buffer zone 40, theservo controller may utilize an OD buffer zone gray coded physicalboundary TKID (e.g. 499).

Continuing on with process 600, if the end track is not within thebuffer zone 40, then at decision block 630 it is determined whether theend track is in a different servo pattern zone than the start track suchthat the servo controller is in the second mode. If not, then an errorhas occurred and the servo controller seek operation restarts.

However, if the end track is in a different servo pattern zone than thestart track, such that the servo controller is commanding the PMR headof the actuator assembly to move across buffer zone 40 then a modifiedor adjusted physical gray coded TKID for the end track that accounts forthe buffer zone 40 is utilized by the servo controller.

For example, as shown in FIGS. 7A and 7B, with reference to Example 3, aseek operation from logical TKID 499 to logical TKID 700 is commanded.However, the servo controller utilizes a modified physical gray code toaccount for the buffer zone such that the servo controller commands aseek operation 720 in which the actuator assembly of the disk drivemoves the PMR head from a starting logical TKID value 499 in servopattern zone 38 (at point 719) (which is the same as the physical graycode TKID value) to actual physical gray code TKID value 1200 in servopattern 36 (shown at point 722) to compensate for the five hundred trackbuffer zone, which is equivalent to the requested logical end track TKIDvalue of 700. In other words, the servo controller adds the buffer zonesize to the seek operation to account for the buffer zone 40. In thisway, the buffer zone is transparent to the rest of the disk drive andhost. The process then ends at block 640.

In this example, by utilizing the previously-described process, theservo controller by using buffer zone characteristics that include abuffer zone starting physical TKID gray code value of 500, a buffer zoneending physical TKID gray code value of 1000, and a buffer zone size of500 tracks, the buffer zone that has been written to the disk duringservo-writing is accounted for during seek operations by theservo-controller in a transparent fashion.

It should be appreciated that these are only exemplary numbers forillustrative purposes. Further, it should be apparent to those of skillin the art that the same or similar processes would work in oppositedirections, as well. For example, if the servo controller was commandedto move the PMR head from a start track in servo pattern 36 to an endtrack in servo pattern 38, the buffer zone size would also be accountedfor. Briefly, in this case, the servo controller would utilize amodified physical gray code at the start track to account for the bufferzone such that the servo controller would command a seek operation tomove the PMR head from an actual physical TKID value in servo patternzone 36 to a logical TKID value (that is the same as the actual physicalgray code TKID value) in servo pattern 38 and during the seek operationwould thereby compensate for the five hundred track buffer zone. Inother words, the servo controller would still add the buffer zone sizeduring the seek operation to compensate for the buffer zone 40, going inthe opposite direction.

Thus, as described above, the servo controller may account for thebuffer zone in a transparent fashion to the rest of the disk drive andhost by using buffer zone characteristics such as, a buffer zonestarting physical TKID gray code value, a buffer zone ending physicalTKID gray code value, and a buffer zone size, to account for the bufferzone that was previously written to the disk during servo-writing duringseek operations.

For example, these buffer zone characteristics may be stored in a tablefor use by the servo-controller during seek operations. The servocontroller may utilize the buffer zone characteristics in mappingoperations between logical TKIDs and actual physical gray coded TKIDsfor seek operations, and in PID control, as well as in other forms ofcontrol. For example, in order to seek over the buffer zone the correctdistance may be used (based on actual physical gray code values on thedisk) rather than based on logical TKID values. In some operations,these values may be persistently fed to the servo control system forcontrol purposes. These operations are performed by the servo controllerin a transparent fashion to the rest of the disk drive and the hostsystem.

As previously described, by servo writing a disk from the ID to the MDand then from the OD to the MD (or vice-versa) with a buffer zonetherebetween, a disk can be formatted utilizing perpendicular mediarecording (PMR) technology (i.e. the head being a PMR head and writingwith a perpendicular flux) in order to avoid unreadable servo sectorsdue to high skew angles, as previously described. By utilizing thepreviously-described servo methodology, the servo controller compensatesfor the buffer zone created in a seamless fashion such that it is hiddenwith respect to the rest of the disk drive system and the host. This maybe implemented by simple servo controller code implementation withoutthe need to change any of the other components of the disk drive system.

While embodiments of the present invention and its various functionalcomponents have been described in particular embodiments, it should beappreciated that the embodiments can be implemented in hardware,software, firmware, middleware, or a combination thereof and utilized insystems, subsystems, components, or sub-components thereof. Whenimplemented in software, or firmware, the elements of the embodiments ofthe invention are the program/instruction/code segments to perform thenecessary tasks.

The program, instruction, or code segments may be stored in a processorreadable medium or transmitted by a data signal embodied in a carrierwave, or a signal modulated by a carrier, over a transmission medium.The “processor readable or accessible medium” may include any mediumthat can store, transmit, or transfer information. Examples ofaccessible media include an electronic circuit, a semiconductor memorydevice, a read only memory (ROM), a flash memory, an erasable ROM(EROM), a floppy diskette, a compact disk (CD-ROM), an optical disk, ahard disk, a fiber optic medium, a radio frequency (RF) link, etc. Thecode segments may be downloaded via computer networks such as theInternet, Intranet, etc. The processor readable or accessible medium mayinclude data that, when accessed by a processor or circuitry, cause theprocessor or circuitry to perform the operations described herein. Theterm “data” herein refers to any type of information that is encoded formachine-readable purposes. Therefore, it may include programs, code,data, files, etc.

The methods described previously can be employed for disk drives withembedded servo systems. However, numerous alternatives for disk driveswith similar or other media format characteristics can be employed bythose skilled in the art to use the invention with equal advantage toimplement these techniques. Further, although the embodiments have beendescribed in the context of a disk drive with embedded servo sectors,the invention can be employed in many different types of disk driveshaving a head actuator that scans the media.

1. A disk drive comprising: a moveable head operable with aperpendicular flux; a disk having a plurality of tracks, each trackhaving a plurality of servo sectors utilized in seek operations, whereinthe servo sectors of the disk include a first servo pattern between oneof an inner diameter (ID) or an outer diameter (OD) of the disk and amiddle diameter (MD) of the disk, respectively, and a second servopattern between the other of the OD or the ID of the disk and the MD ofthe disk, respectively; and a servo controller to control seekoperations with the moveable head, the servo controller to operate in afirst mode when seeking within one of the first or second servo patternsand a second mode when seeking between the first servo pattern and thesecond servo patterns.
 2. The disk drive of claim 1, wherein a bufferzone is present between the first servo pattern and the second servopattern proximate the MD of the disk.
 3. The disk drive of claim 2,wherein the buffer zone includes an area that has been written to withboth the first servo pattern and the second servo pattern.
 4. The diskdrive of claim 3, wherein buffer zone characteristics are determinedupon power-up of the disk drive.
 5. The disk drive of claim 4, whereinthe buffer zone characteristics further include a buffer zone startingtrack identifier and a buffer zone ending track identifier.
 6. The diskdrive of claim 3, wherein the servo controller stores buffer zonecharacteristics including a buffer zone size.
 7. The disk drive of claim6, wherein, in the second mode, the servo controller controls a seekoperation between a first track of the first servo pattern and a secondtrack of the second servo pattern based upon an adjusted gray code valuefor the second track that accounts for the buffer zone size.
 8. The diskdrive of claim 2, wherein the buffer zone is less than approximatelythree-hundred tracks wide.
 9. The disk drive of claim 1, wherein thehead is approximately trapezoidally-shaped.
 10. A method for performingseek operations in a disk drive comprising: moving a head operable witha perpendicular flux relative to a disk, the disk having a plurality oftracks, each track having a plurality of servo sectors utilized in seekoperations, wherein the servo sectors of the disk include a first servopattern between one of an inner diameter (ID) or an outer diameter (OD)of the disk and a middle diameter (MD) of the disk, respectively, and asecond servo pattern between the other of the OD or the ID of the diskand the MD of the disk, respectively; and controlling the movement ofthe head in both a first mode and a second mode to perform seekoperations, wherein, in the first mode, the movement of the head for aseek operation is within one of the first or second servo patterns and,wherein, in the second mode, movement of the head for a seek operationis between the first servo pattern and the second servo pattern.
 11. Themethod of claim 10, wherein a buffer zone is present between the firstservo pattern and the second servo pattern proximate the MD of the disk.12. The method of claim 11, wherein the buffer zone includes an areathat has been written to with both the first servo pattern and thesecond servo pattern.
 13. The method of claim 11, further comprisingdetermining buffer zone characteristics upon power-up of the disk drive.14. The method of claim 11, further comprising storing buffer zonecharacteristics including a buffer zone size.
 15. The method of claim14, wherein the buffer zone characteristics further include a bufferzone starting track identifier and a buffer zone ending trackidentifier.
 16. The method of claim 14, wherein, in the second mode,further comprising controlling a seek operation between a first trackand a second track based upon an adjusted gray code value for the secondtrack that accounts for the buffer zone size.
 17. The method of claim11, wherein the buffer zone is less than approximately three-hundredtracks wide.
 18. The method of claim 10, wherein the head isapproximately trapezoidally-shaped.
 19. In a disk drive including a headand processor-readable medium having stored thereon instructions, whichwhen executed by a processor of the disk drive, causes the disk drive toperform operation comprising: moving a head operable with aperpendicular flux relative to a disk, the disk having a plurality oftracks, each track having a plurality of servo sectors utilized in seekoperations, wherein the servo sectors of the disk include a first servopattern between one of an inner diameter (ID) or an outer diameter (OD)of the disk and a middle diameter (MD) of the disk, respectively, and asecond servo pattern between the other of the OD or the ID of the diskand the MD of the disk, respectively; and controlling the movement ofthe head in both a first mode and second mode to perform seekoperations, wherein, in the first mode, the movement of the head for aseek operation is within one of the first or second servo patterns and,wherein, in the second mode, the movement of the head for a seekoperation is between the first servo pattern and the second servopattern.
 20. The processor-readable medium of claim 19, wherein a bufferzone is present between the first servo pattern and the second servopattern proximate the MD of the disk.
 21. The processor-readable mediumof claim 20, wherein the buffer zone includes an area that has beenwritten to with both the first servo pattern and the second servopattern.
 22. The processor-readable medium of claim 20, furthercomprising instructions to determine buffer zone characteristics uponpower-up of the disk drive.
 23. The processor-readable medium of claim20, further comprising instructions to store buffer zone characteristicsincluding a buffer zone size.
 24. The processor-readable medium of claim23, wherein the buffer zone characteristics further include a bufferzone starting track identifier and a buffer zone ending trackidentifier.
 25. The processor-readable medium of claim 23, wherein, inthe second mode, further comprising instructions to control a seekoperation between a first track of the first servo pattern and a secondtrack of the second servo pattern based upon an adjusted gray code valuefor the second track that accounts for the buffer zone size.
 26. Theprocessor-readable medium of claim 20, wherein the buffer zone is lessthan approximately three-hundred tracks wide.
 27. The processor-readablemedium of claim 19, wherein the head is approximatelytrapezoidally-shaped.